This disclosure relates to a method for calibrating a control algorithm of a clutch control unit of a vehicle. The disclosure also relates to a vehicle comprising a clutch and a clutch control unit, wherein the control algorithm of the clutch control unit is arranged to be calibrated. The disclosure is advantageous in the field of clutch control systems for all types of vehicles with automatic or semi-automatic transmission. The disclosure also relates to a computer program, a computer program product and a computer system.
A clutch is a mechanical device used to connect two rotating shafts. When the clutch is engaged, the shafts are locked to each other and torque can be transferred from one shaft to the other. When the clutch is disengaged, the shafts are completely decoupled and no torque is transferred between them.
Automatic and semi-automatic transmission generally comprises a mechanical clutch, a clutch actuating mechanism and a clutch control unit that controls the torque transmitting capacity of the clutch by means of the clutch actuating mechanism.
In vehicles, a clutch may be used to control the transfer of torque from the engine to the stepped gear transmission system. Before a gear shift, the clutch has to be disengaged, and after the gear shift reengaged. In order to retain the driving comfort during gear shift, e.g., to avoid jerking and unpleasant sounds from the engine, the clutch torque transmitting capacity has to be smoothly controlled during disengagement and engagement of the clutch. However, after aging and wear of components, the clutch may suffer from disturbances and may not react as when new.
A known concept for reducing such disturbances is to introduce a process for learning the clutch off point, as described in is described in WO 2010/090196. The clutch off point, also known as touch point, engagement point, slip point or kiss point, is the physical position at which the clutch engages/disengages, i.e. stops/starts to deliver torque from the engine to the transmission.
However, there are still room for improvements in clutch systems of vehicles with automatic or semi-automatic transmission in order to remove the above mentioned disturbances due to changes in clutch system characteristics as well as adapting clutch systems to the unique characteristics of each individual clutch unit.
It is desirable to provide a method for calibrating a control algorithm of a clutch control unit where the previously mentioned problem is at least partly avoided.
This disclosure concerns a method for calibrating a control algorithm of a clutch control unit of a vehicle, in order to adapt the timing of the clutch control unit to the speed of the clutch system. The method comprises:                requesting clutch disengagement or engagement;        monitoring clutch actuator position;        determining a time interval that starts with said clutch disengagement or engagement request and ends when said clutch actuator has reached a predetermined position; and        calibrating an estimated time interval of the control algorithm, which time interval starts with clutch disengagement or engagement request and ends when the clutch actuator has reached a predetermined position, based on said determined time interval.        
Thus, the method first determines the actual time interval between the request and the clutch reaching the predetermined position. Secondly, the clutch control algorithm is calibrated with this time interval. Thus the control algorithm is adapted to the actual speed of the clutch system, which results in improved timing of the engagement and disengagement of the clutch. The timing of engagement and disengagement of the clutch is crucial in order to smoothly control the torque during a gear shifting process, and thus also crucial to the driving comfort in connection to gear shifting.
The speed of a specific clutch system depends on the characteristics of the individual components in the system, such as springs, cylinders, control valve and compressed air pressure. Even apparently identical clutch systems from the same manufacturer tend to differ slightly from each other since no individual component is exactly identical to another, for example due to manufacturing variations. Furthermore, the actuation speed of a clutch changes during its lifetime as the components age and wear.
In a vehicle with a manual transmission system, the experienced driver adapts to the present characteristics of the clutch system and adjusts the clutch movements accordingly in order to achieve proper timing. But in a vehicle with an automatic or semi-automatic transmission, the clutch movement is automatic and has traditionally been based on fixed parameters. If the characteristics of the individual clutch system are not correctly reflected in the fixed parameters, the clutch movements will suffer from bad timing, resulting in poor driving comfort. Also an initially perfectly timed fixed parameter clutch system will eventually suffer from bad timing, as the characteristics of its components change due to ageing and wear. Thus, in order to achieve proper timing with an automatic clutch, there is an apparent need to adapt the clutch control algorithm to the actual characteristics of the clutch system.
The disclosure further concerns a corresponding computer program, a corresponding computer program product, a corresponding computer system for implementing the method, and a corresponding vehicle comprising a clutch and a clutch control unit.
The time interval determined with this method is defined to end when the clutch actuator has reached a predetermined position. This predetermined position of the clutch actuator may preferably correspond to a predetermined clutch torque transmission capacity. Even more preferably, said predetermined position may correspond to a position where the clutch torque transmission capacity becomes substantially zero during clutch disengagement, i.e. the clutch disengagement point. The clutch disengagement point is of specific interest in clutch control, and thus it is especially useful to know the time it takes to reach it when a request has been made.
The time interval may advantageously be determined at vehicle standstill in order to eliminate potential disturbance sources that may occur during driving, but the time interval may also be determined during driving of the vehicle.
A plurality of determined time intervals may be collected, followed by calculating an average time interval based on the plurality of determined time intervals, and calibrating the clutch control unit based on the calculated average time interval. Such an averaging procedure limits the measurement errors and uncertainties in the determination of the time interval
Preferably, the monitored clutch disengagement or engagement is executed at its currently maximal possible speed, i.e. the clutch actuating mechanism should operate at its maximum speed. The speed of the clutch actuating mechanism obviously affects the determined time interval. Using maxis al possible speed fixes one of the variables that affect the length of said time interval, and the calibration of the clutch control unit is thus rendered easier.
The clutch actuator may be located at a completely engaged position at time of the clutch disengagement request, and at a predetermined disengaged position at time of the clutch engagement request. The completely engaged position, which may in a normally engaged clutch correspond to a position determined without any influence by the clutch actuator, is usually the starting position of the clutch actuator when a request for clutch disengagement is made. The predetermined disengaged position corresponds in a normally engaged clutch to a position determined by the clutch actuator, and is a position where the clutch exhibits zero torque transmission capacity but not necessarily as far as the clutch plate may travel as this over time would risk permanent deformation of the clutch springs. The predetermined disengaged position is usually the starting position of the clutch actuator when a request for clutch engagement is made. For this reason, the completely engaged position and the predetermined disengaged position of the clutch actuator constitute suitable starting points in determining the time interval used for calibrating the clutch control unit.
The clutch may be arranged between a propulsion unit and a gear box of the vehicle.
The vehicle may comprise an automated friction clutch arrangement having a friction clutch, a clutch actuating mechanism and a clutch control unit, wherein the clutch may be disengaged and engaged by the clutch actuating mechanism.
Further, the clutch actuating mechanism may be powered by pressurised air supplied from a pressurised air storage tank, and in such case the estimated time interval of the control algorithm may be calibrated based also on current gas pressure within the gas storage tank. Incorporating the gas pressure dependence of the clutch actuating mechanism in the clutch control algorithm would be advantageous since the gas pressure affects the speed of the clutch actuating mechanism. The clutch position is consequently a function of both the time elapsed since a clutch engagement/disengagement request and the current gas pressure.
The clutch actuating mechanism may alternatively be electrically powered, and in such case the estimated time interval of the control algorithm may be calibrated based also on current and/or voltage supplied to the clutch actuating mechanism. Incorporating the voltage dependence of the clutch actuating mechanism in the clutch control algorithm would be advantageous since the voltage affects the speed of the clutch actuating mechanism.
The estimated time interval of the control algorithm may be calibrated based also on current temperature of the clutch components and/or current ambient temperature of the vehicle and/or clutch actuating mechanism. Thermal expansion and other temperature dependent phenomena in the components may at et the speed of the clutch actuating mechanism and thus the time required to engage or disengage the clutch. Incorporating the temperature dependence of the clutch actuating mechanism in the clutch control algorithm would therefore be advantageous since the temperature affects the speed of the clutch actuating mechanism.
The clutch actuating mechanism may comprise a directional control valve. The directional control valve governs the clutch actuator, which in turn controls the position of the clutch.
The friction clutch may be passively engaged by spring pressure, i.e. a so called normally engaged clutch. Being passively engaged by spring pressure means that the clutch is engaged by the force from one or more springs unless the clutch actuator actively exerts a force in a direction opposite to the spring force in order to brine the clutch to a disengaged position. As soon as the clutch actuator force is released, the spring force will return the clutch to its engaged position.
The opposite construction—a clutch passively disengaged by spring pressure, i.e. a so called normally disengaged clutch—would also be feasible. This means that the clutch is disengaged by spring force unless the clutch actuator actively exerts a force in a direction opposite to the spring force in order to bring the clutch to an engaged position. As soon as the clutch actuator force is released, the spring force will return the clutch to its disengaged position
The clutch actuator position may be determined by means of a position sensor. A measurement of the clutch actuator position gives an indirect measurement of the clutch position, as the clutch actuator and the clutch are mechanically interconnected.